%0 Journal Article
%A Fajardo, A.
%A McIntire, E.J.B.
%T Reversal of multicentury tree growth improvements and loss of synchrony at mountain tree lines point to changes in key drivers
%B Journal of Ecology
%D 2012
%V 100
%P 782-794
%N 3
%X 1. Altitudinal tree line ecotones (ATE) are among the most sensitive
plant formations facing global warming as the altitudinal decrease
in temperature is considered the driver controlling the upper elevation
limit of tree lines world-wide. In this study, we attempted to answer
the following questions: (i) how have the conditions during the last
2-3 centuries affected ATE tree growth (physiology) and recruitment
(demography)? and (ii) how strong is synchrony between these two
processes at the ATEs? 2. We used spatial sampling grids at different
ATEs in two ecosystems on two subcontinents: Nothofagus pumilio in
the Andes of Chilean Patagonia (46° SL) and Pinus albicaulis in the
Rockies of Western Montana, USA (46° NL). Basal increment cores were
extracted from trees to estimate the growth and recruitment date.
An annual detrended basal area increment was estimated for each tree
and was modelled against elevation and time. 3. Tree growth improved
over multiple centuries at all tree lines. Recently (c. 50 years),
however, improvements are disappearing or reversing. The uppermost
tree line trees showed moderate declines in Montana and incipient
declines in Patagonia. The declines are most dramatic slightly below
current tree line (c. 200 m). Tree recruitment patterns showed that
tree lines have been moving uphill in both regions until at least
40-70 years ago. These movements occurred primarily through abrupt
pulses upward with infilling occurring concurrently (Patagonia) or
at some time thereafter (Montana). 4. Synchrony between growth and
recruitment occurred in the 18th and 19th centuries in both regions.
This synchrony was negative in Patagonia and positive in Montana,
with varying lag periods. During the 20th century, these patterns
of synchrony were lost at all sites. This loss of synchrony suggests
that we could be entering a global period in which temperature is
no longer the dominant driver of key features of tree lines. 5. Synthesis.
Our study shows that at two structurally different tree lines, recent
and initial declines in growth and losses of long-term synchrony
are occurring in the latter part of the 20th century. These findings
are opposite to simplistic expectations of global warming effects
on tree line dynamics and call for a model reformulation that uncouples
drivers of growth and recruitment.
%K altitudinal gradients Chile climate change Nothofagus pumilio Patagonia
Pinus albicaulis plant-climate interactions tree line ecotone
%# amriv2
%Z timestamp=(2012.04.16)
%U http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2012.01955.x/full
%F FajardoMcIntire2012
%3 BibTeX type = ARTICLE